A DC motor-driven fan is a relatively simple and well-known mechanism used to circulate air. In common applications, the fan blows the air through a heat exchanger, such as a radiator, condenser or evaporator, or through an air filter. The air that flows through the heat exchanger may be used as a source of heating or cooling, for example in a car's heating, ventilation and air conditioning (HVAC) system or in regulating the temperature of a car's engine, motor, or battery pack. Typically when the fan is being used with an air filter, the assembly is used to circulate air within a relatively confined region, such as the fan assemblies that are used to draw air in and out of a computer case.
There are a variety of techniques used to control the operation of a fan, in particular the speed of a DC fan motor. Fan speed control is desired for a variety of reasons, including minimizing fan noise, minimizing power consumption, and increasing fan motor reliability and lifetime. The simplest control technique uses an on/off switch that may be either manually or automatically controlled. If speed control is required with such an approach, a rheostat may be added to the circuit, thereby providing control over the DC voltage supplied to the fan. Pulse-width modulation (PWM) is another approach routinely used to control fan motor speed. Controllers using PWM switch the power to the fan motor on and off at a fixed frequency, while adjusting fan speed by varying duty-cycle, i.e., pulse width.
While the above control techniques as well as others have been used for years to control fan speed, different fan control techniques are desired that can be used to reliably monitor and control fan speed as well as provide insight into current fan assembly operation. The present system provides such a controller.